Document copying machines often require that a document be held in a stationary manner face down on a document glass in order to be copied. Frequently, in a convenience copier of this type, it is necessary for the operator to place the document on the document glass manually. However, it has also been recognized that it is desirable to afford the operator the opportunity to place a stack of documents upon a feed tray and have the machine feed these documents one-at-a-time onto the document glass for the copying operation. Mechanisms of this type are known as automatic document feeds (ADF).
A serious problem confronted by machines which attempt to automatically feed cut sheets of paper serially to a processing mechanism is the difficulty encountered in avoiding a multiple-sheet feed. While many different kinds of cut-sheet feed devices have been invented and many improvements have been made, the multiple-sheet feed problem remains and is particularly serious in automatic document feed mechanisms for a convenience copier due to the fact that a stack of sheets to be copied can contain various weight paper ranging from light-weight "onionskin" paper to much heavier bond paper.
One of the most successful paper feed devices is the so-called "wave generator" wheel or "shingler" wheel whose operation causes the paper stack to be moved from its stacked condition to a fanned out "shingled" state. In the shingled state, a pair of feed rolls can then reliably grasp the topmost (or bottommost) sheet which has been moved further than the other sheets and send it to the processing station. However, while the fanning out action of the wave generator wheel is very reliable, double-sheet feeds can still occur, particularly where the next sheet sticks to the sheet being fed. Such sticking is typically caused by static electricity. As a consequence, a major benefit of the present invention is to provide against multiple-sheet feeding in an automatic document feed. This benefit has been achieved through a unique arrangement of the guides in the paper path together with a restraint pad.